1. Field of the Invention
This invention relates to the epitaxial growth of III-V layers and to the doping thereof, and, more particularly, to the use of a single doping source for providing a wide range of doping concentration.
2. Description of the Prior Art
The AsCl.sub.3 /Ga/H.sub.2 vapor phase epitaxy (VPE) system has been extensively used for preparing GaAs epitaxial layers for field effect transistor (FET) devices in the past few years. The key to success of device quality GaAs material lies in the ability to control background impurity, surface morphology, thickness and doping. These are strongly influenced by growth conditions such as temperature, substrate orientation, growth rate and the AsCl.sub.3 /H.sub.2 ratio. The most commonly used n-type dopants in GaAs are sulfur and silicon and these are frequently introduced by means of dilute H.sub.2 S/H.sub.2 or SiH.sub.4 /H.sub.2 gaseous mixtures, respectively. Both of these sources are subject to control limitations because of instabilities which limit their shelf life. Additional doping sources include the liquid doping source S.sub.2 Cl.sub.2 /AsCl.sub.3 and solid SiCl.sub.4 at -147.degree. C.
The use of gaseous solutions requires the metering of small gas streams, while liquid solutions have heretofore suffered from short shelf life or have not been readily prepared with reproducible compositions.